Internote coupling means for an electropiano



Fi led May ,27, 1966 Sept. 30, 1969 wQ RTm ET AL 3,470,305

- INTERMOTE COUPLING MEANS FOR AN ELECTROPIANO 2 Sheets-Sheet 1 I NVENTOR DAN/EL W MAW/NAN!) JAMES F ZIEGLEE,

ATTORNEYS y m m. 1Z6,

Sept. 30, 1969 o. w. MARTIN ET AL 3,470,305

INTERMOTE COUPLING MEANS FOR AN ELECTROPIANO Filed May 2'7, 1966 2Sheets-Sheet a Fig. 3

' INVENTOR flA/v/a 14/ MAPT/NAND Y JAMES E Z/EGLEE,

BY @WM 71%. (m 2% ATTORNEYS United States Patent ice 3,470,305 INTERNOTE COUPLING MEANS FOR AN ELECTROPIANO Daniel W. Martin and James F.Ziegler, Cincinnati, Ohio, assignors to D. H. Baldwin Company,Cincinnati, Ohio,'a corporation of Ohio Filed May 27, 1966, Ser. No.553,335 Int. Cl. G01h 3/00 US. Cl. 84-1.16 9 Claims ABSTRACT OF THEDISCLOSURE An electrical musical instrument, such as an electropiano,wherein the mechano-electric transducers for a series of strings aremechanically interconnected, as by means of a coupling plate, so as toprovide sympathetic vibration between strings tuned for different notesof the scale.

The term electropiano as used herein means an instrument having a stringplate, strings thereon and an action whereby the strings may be set inmotion, but devoid of a sounding board, while having means whereby thevibrations of the strings can be converted directly into electricalpulsations. The electrical pulsations, with such amplification as may bedesired, are then converted into sound by one or more loud speakers.While the invention is not so limited, there has been felt a need for alarge concert instrument of the electropiano type, so that the soundoutput of the instrument can be regulated in accordance with the soundoutput, say, of a symphony orchestra.

The present invention will therefore be described in connection with aconcert grand type of instrument. It will be evident that the tonesproduced by such an instrument must closely match the tones of theconventional acoustical grand piano. While it is not difficult toconvert the vibrations of strings into electrical pulsations, greatdifficulty has been experienced in achieving a true piano tone quality,and much work has been done in this field. Among the various transducerswhich may be used, piezoelectric crystals and barium titanate ceramicelements, coupled to the string terminations, have been found quiteeffective in converting all of the modes of mechanical movement of thestrings which are ordinarily converted to acoustical energy by thesounding board of conventional instruments. In United States Patent No.2,334,744, Hugo Benioff used metal elements supported by the strings astermination means for the speaking length of the strings. The elementshad sufficient mass for the purpose. Mounted on the termination meanswas a cantilever element for each string or note-group of strings, witha piezoelectric crystal interposed between the cantilever element andthe body of the termination means. This effected some improvement, butstill presented a number of difficulties.

In an acoustical piano, the strings are set into motion by the hammersof the action, which immediately after striking the strings, come out ofcontact with them. The tone, at first at a high sound level, decaysquickly due to various damping factors inherent in the instrument. Oneof these factors arises, of course, from the fact that the string mustdrive the sounding board through the medium of the bridge. But there areother damping factors which must be taken into account, including thetermination of the strings and the speaking length thereof. These haveto do in part with the nature of the plate and its appurtenances.

The decay of the tones occurs in a complex and distinctive manner,exhibiting a greater rate of decay at the start than later on in thetone. Moreover, the decay rate is not the same for the differentfrequency components 3,470,305 Patented Sept. 30, 1969 making up thetone produced by any given string or group of strings tuned to the samefundamental frequency.

Yet again, when the dampers are raised by the action of the sustainingpedal, there is in the acoustical piano a certain amount of interactionbetween the strings of notes of different frequencies. The interplay ofthese factors is extremely complex. Suffice it to say, that theacoustical piano as an instrument has distinct qualities of tone andvoice which are recognizable. If these are departed from in anelectropiano, the result is generally unfortunate since the basicpurpose of concert electropianos, at least, is the control of the volumeof the sound produced without departure from the recognized tonalquality of the instrument.

Benioff, in a later United States Letters Patent No. 3,049,958,endeavored to achieve, in his transducers, damping and other effectssimilar to those of a sounding board and bridge. A considerableimprovement was achieved. Nevertheless the problem of providingsympathetic vibrations in adjacent strings or string groups, especiallywhen the sustaining pedal is depressed, was not solved. There was also atendency for the tones in the bass and tenor ranges to run together whenplayed in rapid sequence (such as runs and arpeggios) with the damperpedal depressed.

Burkhard and Sabine in their United States Patent No. 3,069,955 alsosought to achieve enhanced tonal quality in an electronic piano bydamping groups of the strings (in a single string per note instrument)by means of resiliently supported weights mounting string contactingrigid bridge members, the weights acting to damp the fundamentalfrequencies at a higher rate than the higher partials, thereby tendingto simulate the damping effects obtained in an acoustical piano. Suchweights are interposed as separate and additional bridge membersintermediate the string mounting bridges Which define the speakinglengths of the springs, with the transducers remote both from theweights and bridges. This arrangement, with its multiple point stringcontact, interposes numerous problems of string tuning and theinterjection of rattles and other extraneous noises during stringvibration.

In contrast to the foregoing prior art, the instant invention providesan electropiano wherein the aforementioned difficulties are effectivelyreduced or eliminated, the invention contemplating a simplifiedconstruction wherein only two points are involved in positioning thespeaking portion of each string, with all string modes of vibration,including non-selective bridge coupling between the strings, controlledat the termination of the strings rather than at a point or points alongtheir speaking lengths. Thus, resonant loading and associated dampingare applied to the strings at the ends of their tuned lengths, with aresiliently mounted and damped mass serving as the termination for thetuned length and additionally incorporating the transducer elements.

It is also a basic object of the invention to provide a more naturaldouble-decay rate in the tones of the instrument.

It is an object of the invention to mount groups of transducers on amember which will be sufficiently massive to terminate the speakingportion of each string effectively, but which at the same time willpermit sympathetic vibrations to occur between adjacent strings.

It is an object of the invention to mount a string terminating member orsupport in such a way that it will resonate at a low frequency, sayc.p.s., and to damp the resonance through mechanical resistance, in sucha way that the lower partials of the tone decay more rapidly than thehigher partials.

It is another object of the invention to control not only the shape ofthe decay curve and the duration of the decay period, but to providemeans for controlling the relative intensity of the fundamental andpartials during the decay period.

Important objects of the invention may be summarized as the provision ofmore realistic and piano-like tones in electropianos, the provision oftones characterized by more rapid damping in the lower partials than inthe higher partials, the provision of damping which essentially has thesame effect as the damping in an acoustical piano, and the provision ofinternote coupling in electropianos having no sounding board, especiallywhen the dampers are lifted from the strings by the damper pedal.

These and other objects of the invention which will be set forthhereinafter or will be apparent to the skilled worker in the art uponreading these specifications, are accomplished by that structure andarrangement of parts of which an exemplary embodiment will now bedescribed. Reference is made to the accompanying drawings wherein:

FIGURE 1 is a plan view of the frame or plate of a grand piano includinga partial showing of the stringing and the mounting of the transducersas in the Benioff Patent No. 3,049,958.

FIGURE 2 is a perspective view of a single transducer, to be used inaccordance with this invention in the hereinafter set forth.

FIGURE 3 is a side elevation showing the mounting of transducers in away to secure the benefits of this invention.

FIGURE 4 is a semi-diagrammatic perspective view with parts in section,of another embodiment of the invention.

Although the bridge of a conventional piano has a certain rigidity, itis compliant when compared to a solid metal plate. Thus while thetermination means for the speaking length of strings in an acousticalgrand piano are rigid in theory, there is sufficient vibration at theterminations to drive the bridge and soundboard, and to producesympathetic vibrations in springs or strings or string groups other thanthe strings which are struck. In an electropiano there is noconventional bridge and no sounding board; and the termination of thespeaking lengths of the strings may be very much more rigid.

The string plate of a grand piano is illustrated at 1 in FIGURE 1. It isusually, although not necessarily, in the form of a casting. The castinghas a front portion 2 and a rear portion 3, which portions areinterconnected by ribs 4, 5, 6, 7 and 8. The front portion of the plateis configured to accept a pin block indicated at 9.

The front portion of the string plate with pin block attached isfrequently mounted above the front portion of the grand piano case (notshown), while peripheral portions of the string plate lie inside theouter rim of the grand piano and are fastened to the inner rim, againnot shown.

FIGURE 1 illustrates a typical grand piano plate; but other platestructures may be employed. The electropiano, of course, lacks anysounding board or bridge. The plate will be supported in the piano caseat such a height that an action having upwardly striking hammers willcoact with the strings to set them into vibration as known in the art.The action itself is not illustrated in FIGURE 1, excepting for theindividual string dampers 9a. The strings extend from hitch pins, suchas those indicated at 10 on the rear portion of the string plate,forwardly over agralfe means 11 also positioned on the plate. Thence,they pass over a series of transducers 17 which effectively terminatethe tuned length of the strings at the rear. The forwardly extendingstrings may pass over additional agraffe means 12 and 12a at the frontportion of the string plate, and are ultimately engaged by the tuningpins 14 in the pin block 9. A series of treble strings is indicated at13, certain intermediate strings at 15 and a series of bass strings at16. The agraife means 12 effectively terminate the tuned length of thestrings at the front of the .4 string plate, and may be of variousforms. They may be like the agraife means 11; but other means may beemployed if desired, such as brass elements having shanks threaded intoopenings in the string plate and provided with holes through which thestrings pass.

In the piano of the Benioff Patent No. 3,049,958 the transducers 17 weremounted to a heavy plate (or mechanical ground) which in turn wasrigidly mounted to the rear portion of the string plate or to anextension thereof. The patentee endeavored to simulate the decaycharacteristics of the tones of conventional or mechano-acoustic pianosby providing in the transducers themselves an amount of damping whichwould be substantially equivalent to the damping effects of a soundingboard and bridge. Quite pleasing tones were secured in this way; but theeffects were imperfect for a number of reasons. For one thing, theinteraction of a vibrating string (or strings) upon other piano stringsin the assembly was not adequately achieved. In other words, thecoupling between the strings of a grand piano which occurs through thebridge and the sounding board in an acoustical piano was essentiallyabsent. In the earlier Benioif patent where the transducers were mountedon blocks which were suspended from the strings, a degree of couplingcould have been achieved if the blocks had been elongated so as tocontact a plurality of strings having different frequencies. But thecoupling effect in that patent tended to be too great as respects thosestrings having pickups mounted on the same base, and absent as tostrings not so directly coupled; and it was not possible to extend thecoupling in any such way as was accomplished in the acoustic piano bythe bridge. In the second place, the decay of the tones was not entirelypiano-like for reasons which will later be set forth.

Nevertheless, the type of individual transducer used by Beniotf inPatent No. 3,049,958 is suitable for the purpose of this invention andwill now be described as exemplary. Referring to FIGURE 2, thetransducer means comprises a block of metal 18 fastened to a base member19 and provided with a cantilever arm 20. This cantilever arm is reducedin thickness as at 21. It carries a head portion 22 which is hollow asviewed from above and which furnishes one of the clamping means for aseries of strings 23, 24 and 25. These three strings may be consideredas tuned to substantially the same frequency. As is Well known, themiddle and upper registers of a grand piano have usually three stringsper note. In the tenor section in the scale of the piano, the number ofstrings per note will be reduced to two, while in the bass section therewill be a single string per note. As is also conventional, the stringsin the bass section will usually be wound with wire so as to increasetheir linear density. The type of transducer illustrated in FIGURE 2 maybe used for single, double or triple strings.

The strings are clamped to the portion 22 of the cantilever arm by anoverhead member 26 in place by screws 27 engaging the head 26.

In order to provide a housing for preventing damage to thepiezo-electric crystal forming a part of the transducer, there ispreferably provided on the base a second block of metal 28 having aforwardly extending arm 29. The block 18 is aflixed to the base 19 bymeans of a threaded member 30, while the block 28 is affixed to the baseby a threaded member 31.

The transducer makes use of a pressure-responsive element 32 (e.g. apiezo-electric crystal) interposed between the cantilever arm 20 and thebase 19. Electrical contact is made to the element by wires 33 and 34which pass downwardly through holes in the base 19 and thence along anyconvenient passage to an output system comprising an amplifier and oneor more loud speakers.

The lower edge of the element 32 is mounted in a groove 35 in the basemember with the interposition of a layer 36 of insulative materialtherebetween. This layer serves two purposes. It insulates the elementfrom the base 19, and it is also of such character as to provide acertain degree of damping. In order to insulate the element from thehead 22 of the cantilever arm 20, use is made of another layer ofdamping material 37 interposed therebetween. The damping material mustbe satisfactorily strong for the purpose. -Its nature can be varied inaccordance with the effect desired. A material of suitable dampingcharacteristics, by way of example, was found to be a resinous materialsold by Astatic Corporation under the trademark Audioid. The dampingmaterial is one which must have a relatively large viscosity or internalfriction in proportion to its density and elastic coefficient. Othermaterials which may be used are silicones, chloroprene and othersynthetic rubber-like material, rubber-cork mixtures, andrubber-saturated fibrous substances.

Transducers as generally illustrated in FIGURE 2 and as described hereinhave been found very elfective in converting the mechanical modes ofmotion of the vibrating strings into pulses of electrical energy. Butwhen, as set forth in Patent No. 3,049,958, these transducers weremounted solidly upon the string plate or an extension thereof, the decayof the tones of struck strings was found to differ from the decay of thetones of an acoustical piano having a bridge and sounding board. Thereis a tendency in eleotropianos for the decay of the tones to occur at aslower rate than is normal for the acoustical piano. Also the tonaldecay in an acoustical piano is not the same for all partials of thecomplex tone. This does not refer to the strings or string assembliestuned to different frequencies. As the skilled worker in the art willrecognize, when a string is set into vibration it has a mode of motionat a fundamental frequency; but at the same time it has modes of motionat other frequencies, bearing a nearly harmonic relationship to thefundamental frequency. Piano strings also have lengthwise or axial modesof motion.

In the present invention the individual transducers are suspended fromthe strings and collectively support a member which is suflicientlymassive to terminate the tuned portion of the strings eifectively, buttransmissive enough to provide mechanical coupling between strings tunedfor different notes of the scale. The coupling member, further, is ofsuch mass that it will resonate with the combined stilfness of thestrings (and other supporting members) at a low frequency (of the orderof 100 c.p.s.). The resonance is damped through mechanical means to theproper degree for damping low-frequency partials more rapidly than thehigher partials during the decay periods of the piano tones.

In the practice of the invention as shown in FIGURE 3, therefore, aseries of transducers is mounted upon a supporting and coupling plate ofmetal. The best form of transducer known to applicants has beendescribed above in connection with FIGURE 2. It is to be understood,however, that modifications may \be made in the transducer withoutdeparting from the spirit of the invention. The individual transducersas shown in FIGURE 2 are relatively small since they are intended tohandle the string or strings for an individual note of the instrument,to form a rear terminus for the tuned length of such string or strings,and to convert the mechanical modes of motion thereof into electricalimpulses.

In the practice of this invention a series of such transducers ismounted upon a coupling plate of metal. Referring to FIGURE 3, tentransducers 17 are shown mounted upon a coupling plate 38. This is apartial showing since a very large number, if not all, of thetransducers will be fastened to the coupling plate 38. It is possibleand preferable to have one such plate common to all of the transducersin the instrument, but it does not depart from the spirit of theinvention to provide separate plates for dilferent portions of theinstrument, to each of which plates a comparatively large number oftransducers are attached.

The metal plate 38 is preferably formed of steel, such as A181 1018 orA181 8620, the steel having substantially less damping action than wouldbe the case with other metals such for example as cast iron or brass.

The manner in which the individual transducers are fastened to thecoupling plate 38 may be varied. The connection, however, should berigid. It is possible to attach the transducers to the plate 38 byadhesive means such as epoxy resin cement. A preferable mode ofattachment involves prolonging the threaded fastening means 30, 31 ofFIGURE 2, so that they extend below the element 19 of the transducer andare threaded into tapped holes in the plate 38. In this instance theymay pass through clearance holes in the elements 19. Alternatively, thetransducers themselves may comprise the coupling means, the base members19 of the transducers being rigidly connected to each other and the basemembers collectively being of a mass sufiicient to produce the desiredresonance frequency. In such event the interconnected base members actas the coupling plate.

Since the strings of the isstrument are clamped to the severaltransducers as hereinabove described, and since the combination of thetransducers and/or the coupling plate 38 provides sufficient mass, thetransducers are enabled to serve as rear terminations for the tunedlength of the strings of the instrument. At the same time, thetransducers serve as an interconnection between strings or groups ofstrings. In other words, if a string or group of strings representing asingle note in the scale of the instrument is struck by one of thehammers of the piano action, while one or more dampers 9a are raisedfrom the strings, there will be an interaction between the struck stringor strings and other undamped strings or groups of strings in theinstrument. This interaction is not confined to other strings or groupsof strings which bear a strictly harmonic relationship to the struckstrings, but includes a sympathetic vibration of non-harmonicallyrelated strings as well. Such interaction is necessary for theproduction of a true piano-like quality.

Nevertheless, if the coupled combination of transducer elements weremerely suspended from the strings of the instrument, the aforesaidinteraction could be considered excessive because of the low dampingcharacteristics of the structure. Hence, additional damping means areusually required.

A third function of the combination of transducers and connecting platesis to provide a structure which resonates on the strings at a lowfrequency.

The desired resonance at a low frequency is generally a resonance atabout c.p.s., although this may be varied. The resonating characteristicis a function of transverse string stifiness, stiffness of dampingmembers or other members contributing to support of plate 38, and thecombined mass of the coupling plate 38 and the transducers which areattached to it. It may be controlled by the choice of the thickness ofthe plate 38, and of the stiffness of the damping and supporting membershereinafter described. With transducers of approximately the size andproportions illustrated herein, and a plate width of the order of about2 /2 to 3 inches, a plate thickness of about to about A of an inch willinsure resonance at a desirable low frequency. This value is intended tobe illustrative rather than limitative.

The plate 38 rest upon pads 43a and 43b of damping material which inturn rest upon a plate 44. The plate 44 may be rigid and serve asmechanical ground, or it may be fastened by means of screws 45 toanother mass 46 of suificient size to form a mechanical ground.

In the manufacture of pianos, mass 46 may be cast as a part of thestring plate of the instrument; but it is frequently more convenient touse as the mechanical ground the framework of the piano case. A singlemember 46 may be used extending throughout the range of the instrument;but it does not amount to a departure of the spirit of the invention toemploy bar-like pieces of lesser length which are afiixed to the rearportion of the string plate or to the piano case structure. Since themember or members 46 are intended to be so massive as to constitute amechanical ground, the nature of the material from which they are madeis not a limitation on the invention.

There are numerous materials which may be used for the damping elements43a and 43b above described. These materials include felts and otherfibrous materials, Ordinary felts made of animal or vegetable fibershave a tendency to introduce too much damping :at the higherfrequencies. Very good results are obtained by using precom pressedstrips made up of glass fibers lightly bonded together with resinoussubstances. Mats of this type are frequently used for mounting heavymachinery so as to minimize the transmission of vibrations to asupporting floor.

The damping elements 43a and 43b may be in the form of a continuousstrip used throughout the length of the coupling bar 38; but it ischaracteristic of the structures of this invention that the actualdamping may be varied and controlled by using individual pieces orspaced pieces of the damping material beneath the plate 38. Alsoindividual pieces of damping material of differing thickness orcharacteristics may be employed at different points in the scale of theinstrument.

It has been found that the provision of additional stiffness and dampingadjustment means acting to vary resonance frequency and damping alongthe length of the plate 38 will give an even truer piano-like quality tothe tones, and a double-decay characteristic which is substantiallyidentical with that obtained in the coustical piano.

In order to apply the additional stiffness and damping adjustments justmentioned, a preferred form of the structure of this invention shown inFIGURE 4 involves the use of a series of bolts 39 passing throughclearance holes 40 in the portions 19 of the transducers but threadedinto tapped holes in the plate 38. When these bolts are in adjustmenttheir lower ends bottom in depressions 41 formed in the upper surfacesof short metallic bars 42. These bars are preferably common to a smallplurality of transducers. Tlie bars 42 are preferably, but not neces-'sarily, made of steel and rest upon a layer of damping material 43c ofthe character previously described which in turn rests on the plate 44.As before, the damping material may comprise either a single strip, asillustrated, or it may be composed of a plurality of spaced apart pieceswhich may be varied in thickness and damping characteristics.

It will be understood from the structure shown in FIG- URE 4, that afterthe piano has been strung and the strings have been tensionedsubstantially to their desired frequencies, the bolts 39 are turneddownwardly so that they have a bearing in the socket elements 41 of theplates 42. They should bear in these socket elements sufficiently tosupport a portion of the weight of the combination of transducers andcoupling plate 38 upon the stiifness of damping elements 43. It is anadvantage of the described structure that the bolts 39 may beindividually adjusted to vary both the stiffness and the damping indifferent parts of the connector plate 38. Another way in which theresonance characteristics may be varied along the musical scale is tovary the cross-section of plate 38, e.g., by tapering it down toward thetreble end to raise the resonance frequency of the upper end of thescale. In these ways the tonal scale of the instrument may be balanced.

In using the illustrated structure of FIGURE 4 it has been found thatnormal piano tones are produced when the electrical pulsations from thetransducers are amplified and reproduced by loud speakers. Inparticular, the tones, upon analysis, are substantially identical to thetones of comparable acoustical pianos having sounding boards andbridges, and the piano-like tones are substantially independent of thedegree of amplification within reasonable limits. Further, the tones ofthe instrument exhibit the characteristic double-decay of piano tones.When the sustaining pedal is operated to remove the dampers from thestrings, the interaction between struck strings and non-struck stringsis characteristic of an acoustical piano having a sounding board and abridge. The structure herein described eliminates a tendency for notesstruck rapidly in succession (as in arpeggios) to run together; and iteliminates the previously noted tendency of bass notes struck rapidly insuccession to become muddy.

As should now be apparent, the resiliently mounted and damped mass isitself the termination for the tuned lengths of the strings, andconsequently the resonant loading and associated damping are applieddirectly at the ends of tuned lengths rather than by means of a separateand additional bridge; and preferably the transducer elements arethemselves a part of the termination mass which also serves as thetransducer structure. With such arrangement, the damping adjustment hasvery little, if any, effect upon the tuned length of the strings andhence upon string tuning, and there is nothing in contact with thestrings within their tuned segments which would be a vibration node forsome modes of vibration and hence a source of rattles or otherextraneous noises. Because only two contact points are involved inpositioning the speaking portion of each string, the warping of thebridges or frame will not affect the amount of string damping, Whereas athird intermediate separately supported point can add or subtracttransverse stresses to the string where warping occurs. The clamping ofthe strings in accordance with the instant invention also assurestransverse stiffness of the strings at the ends of their tuned lengths.Modifications may be made in the invention without departing from thespirit of it, and consequently it is not intended that the invention belimited other than in the manner set forth in the claims which follow.For example, the resiliently damped coupler plate may be used to defineone end of the speaking length of the strings, with the transducermeans, which will be rigidly mounted, engaging the strings at theopposite ends of their speaking lengths. The instant invention will alsofind utility in an instrument such as a harpsichord in which the stringsare vibrated by a plucking type of action rather than being struck byhammers.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In an electrical musical instrument having a supporting framemounting a string plate, strings supported on said plate and stretchedbetween pairs of points defining tuned string segments, a series ofmechano-electric transducer means contacting the strings comprising aseries of adjoining notes of the musical scale, said transducer meanseach contacting said strings on one point of said pairs of points, meansinterconnecting said series of transducer means, said interconnectedtransducer means serving collectively as a mechanical internote couplingmeans common to the strings of a series of notes in the musical scale,and a damping material interposed between said internote coupling meansand an essentially no-vibratile support forming a part of saidinstrument, the mass of said internote coupling means being sufiicientto terminate the tuned segments of the strings but suflicientlytransmissive to provide sympathetic vibration between strings tuned fordifferent notes of the scale.

2. The structure claimed in claim 1 wherein the means interconnectingsaid series of transducer means comprises a steel plate on which saidtransducer means are mounted.

3. The structure claimed in claim 1 wherein the mass of said internotecoupling means is chosen so that it will resonate at a low frequency,such as c.p.s.

4. The structure claimed in claim 1 wherein the nonvibratile supportcomprises a portion of said string plate.

5. The structure claimed in claim 4 wherein said nonvibratile supportincludes a heavy metal bar attached to and supported by said stringplate.

6. The structure claimed in claim 1 including means for adjusting thebearing of said internote coupling means on the non-vibratile support,

7. The structure claimed in claim 6 wherein said adjustment meanscomprises bearing bolts in threaded engagement with said internotecoupling means, the ends of said bolts bearing against relatively smallmetallic plates seated on the damping material interposed between saidinternote coupling means and said non-vibratile support.

8. In an electrical musical instrument having a string plate, stringssupported on said plate and stretched between pairs of points definingtuned string segments therebetween, mechano-electro transducer meanscontacting the strings at one point of said pairs of points, and amechanical internote coupling means connected to said strings at onepoint of said pairs of points and being common to the strings of a largenumber of notes in the musical scale, the mass of said coupling meanstogether with the transverse stiffness of said strings forming a res- 10onant mechanical system which is sufficient to terminate the tunedsegments of the strings but sufficiently transmissive to providesympathetic vibration between strings tuned for different notes of thescale.

9. The structure claimed in claim 8 including damping means connectingsaid coupling means to a solid element of sufiicient mass to act as amechanical ground, said damping means acting to damp the resonantmechanical system.

References Cited UNITED STATES PATENTS 3,049,958 8/1962 Benioff 84-1.l6

HERMAN KARL SAALBACH, Primary Examiner SAXFIELD CHATMON, JR., AssistantExaminer US. Cl. X.R. 84-1. 14

